Aging has been previously reported to be associated with prolonged plasma half-life of antipyrine. Such age differences, however, could be due to other variables that both influence drug metabolism and differ with age. The purpose of this study was to examine antipyrine metabolism in participants in the Baltimore Longitudinal Study of Aging and to explore the possibility that age differences in such habits as alcohol use, caffeine consumption and cigarette smoking might influence drug metabolism in this population of healthy men.